Advancements in micro- and Nanotechnology have led to a myriad of direct detection schemes and sensitive transducers for biological assays. Indeed, nano-scale transducers with capabilities to detect single cells have already been demonstrated. However, the overall sensitivity of a bio-assay is currently limited by diffusion- based mass transport towards the sensor surface (dictated by the fluidic component), and is typically orders of magnitude worse than the transducer capabilities. This bottleneck will always exist in architectures where the volume concentration of a target molecule or cell is detected along a wall of a fluid-filled compartment - as is customary with micro-fluidics or micro-well plat based assays. As such, none of the state-of-the-art, solution- based direct bio-sensing schemes - such as enzyme-linked immunosorbent assays (ELISA) - can detect less than 103-104 cells/ml. Achieving higher sensitivities require either long incubation periods (hours to days) or lengthy sample amplification. As a result, there is currently no commercial product for rare cell and pathogen detection that can simultaneously achieve a high overall detection sensitivity (i.e., ~10 colony forming units per ml) and a rapid assay completion time (i.e., <10 mins). This shortcoming directly translates into inefficiencies in patient treatment - such as the widespread use of broad-spectrum antibiotics with sepsis and urinary tract infections - that contributes to increased costs, longer hospitalization times and the emergence of drug resistant bacterial and fungal strains. In particular, the need for sensitive and rapid pathogen identification is criticalin the context of sepsis, since each hour lost in targeted treatment results in a 9% increase in patient mortality. Current pathogen identification methods, such as blood cultures or PCR tests, take too long to affect the critical initial decision for treatment selection. Sepsis is the second largest cause of death in non-coronary intensive care units (750,000+ cases, 215,000+ deaths annually in US alone), costing over 17B/year to treat. Here, we propose to overcome the diffusion bottleneck that plagues all existing fluid-based direct bioassays by developing a novel platform that relies on biocompatible magnetic nanofluids for rapid, active and selective transport of target moieties to a given sensor's surface in a label- and labor-free fashion. Our approach can isolate, separate, transport, focus, direct and detect very rare cells or pathogens in an otherwise complex biological fluid sample. Our goal in this Phase I project is to build and demonstrate quantitative, ultra-rapid (<10 min) detection of several pathogens of interest in spiked buffer, broth and blood samples, with sensitivity levels (~10 pathogens/ml) that cannot be obtained by any existing direct detection method. Furthermore, we propose to study and establish the operational parameters of our prototype system and compare its performance with existing ELISA, PCR and blood culture tests. If successful, our system will achieve unprecedented sensitivity and speed, and could have a real impact in point-of-care diagnostics of infectious agents. Our approach could easily translate into better antibiotic stewardship and lower mortality rates in sepsis and other severe infections.